The present invention is directed to method and apparatus for monitoring the brakes of a motor vehicle and providing a warning signal when brake adjustment or repair is needed.
Systems of the type described above are generally known to the art and are illustrated by U.S. Pat. No. 4,583,071 issued to Sebalos et al on Apr. 15, 1986, United Kingdom Patent Specification No. 1,387,808, United Kingdom Patent Specification No. 1,512,003 and in a publication entitled Brake Alert Systems, Inc. Installation and Adjustment Guide. In the known systems a permanent magnet is typically mounted to a rod which is moveable in response to depression of a brake pedal by the operator of a motor vehicle. (As known to those familiar with the art, a push rod in an air brake system travels a distance proportional to brake (lining and drum) wear between brake adjustments corresponding to mechanical "slack" in response to depression of the brake pedal by the vehicle operator). A magnetically actuated switch is fixedly mounted relative to the moveable permanent magnet. In the event that the brake rod travels beyond a certain range, the permanent magnet on the moveable rod will be brought sufficiently close to the magnetically actuated switch to cause actuation thereof. The switch is coupled to signal means, as for example a signal light, and actuation of the signal means provides the operator with an indication that brake adjustment is necessary. In motor vehicles having air brakes, the permanent magnet is most commonly mounted to a preexisting push rod which extends from the diaphragm of an air chamber to a preexisting slack adjuster of the braking system.
The known systems, such as those described above, are powered by a connection to the existing electrical power supply for the vehicle. The signal indicators which are typically indicator lights, are installed on the dashboard of the cab.
In practice, the use of the existing electrical system of the vehicle as the power supply for a brake monitoring system, particularly the brakes of a trailer, is disadvantageous for several different reasons. The need to individually wire and electrically connect the brake monitor system to the vehicle power supply is a time consuming and expensive procedure. The running of individual wires through the chassis of a vehicle subjects the wires to damage as the vehicle operates. If a wire is broken, the vehicle operator will not be provided with a brake signal thereby defeating the purpose of the system. Moreover, this type of brake monitor system will not operate if the vehicle battery is dead or if the vehicle ignition switch is not "on".
In addition to the above, there are particular problems when the known brake monitoring systems are installed to monitor the brakes of a trailer of a tractor-trailer vehicle. The connection of such a system to the existing electrical power system of the vehicle and to signal indicator lights in the cab requires substantial wiring which is disadvantageous for the reasons noted above. Additionally, such systems are dependent upon the integrity of the pre-existing electrical contacts between the tractor and trailer which often are not available or reliable. Moreover, the trailer of a tractor trailer is not independently electrically powered, and thus a brake monitoring system will operate only if either the trailer running lights or the brake lights are actuated.
For the reasons discussed above, known brake monitoring systems operating from the existing electrical power supply of a vehicle are disadvantageous and unreliable in many different respects.
It is an object of the present invention to provide a reliable method and apparatus for monitoring the condition of the brakes of a motor vehicle which overcomes the above noted disadvantages of known brake monitoring systems. In particular, it is an object of the present invention to provide a method and apparatus for monitoring the condition of vehicle brakes which does not depend on the existing electrical power system of the vehicle for its operation. In one preferred embodiment of the invention, the brake monitoring system may be installed as a self-contained unit without any external wiring at all. Other objects and advantages of the invention will be apparent from the following description.